@ Banai Lynn Feldstein
"I heard a rabbi explain once, but I only recall some of the story. It was important to remember the yahrzeit, the anniversary of their death."
Quite true. But one also must know at least the week of birth of a male child, so as to celebrate his bar mitzvah at the correct time. A lot of boys were told (or they remembered from their bar mitzvah) that they were born during the week of the <whatever> weekly portion of the Torah.
Sagan/Shagan family from Veliuona (Velon), Lithuania
Goldberg family from Vidukle, Lithuania
Susselovitch/Zuselovitch family from Raseiniai (Rassein), Lithuania